Spark plug



Mmh 2, 1937.

P. K. DEVERS SPARK PLUG Filed Aug. 28, 1935 Inventor: Philip K.Dever-s,

9 4244 8. 9% by His Attorneg.

Patented Mar. 2, 1937 PATENT OFFICE SPARK PLUG Philip K. Devers, Lynn, Mass, assigncr to General Electric Company, a corporation of New York Applicationmlgust 28, i935, Serial No. 38,183 I 5 Claims.

The present invention relates to the construction of spark plugs intended for use in internal combustion engines. In particular, my lnven tion relates to spark plugs'containing insulators of fused silica although it is not restricted in its use to silica insulators.

My invention in some aspects constitutes features of improvement over the spark plugs shown and described in prior U. S. Patent No. 1,869,133 issued on July 26, 1932 to Devers and Hooper.

Although silica possesses superior insulating properties which especially adapt it for use at high temperatures, silica insulators in spark plugs have been found in some cases subject to breakage when under pressure and in operation at temperatures varying over a wide range. I have found that one cause for such breakage is the difference in rate of expansion of the silica and the metal conductor of the plug with its surrounding cement which are imbedded in the duct or passage extending longitudinally through the insulator.

It is the object of my invention to improve the resistance to breakage or cracking of insulators in spark plugs and to improve their electrical characteristics. v

In accordance with one feature of my invention the conductor which extends longitudinally through 'the insulator of a spark plug is sealed to the insulator only at a restricted region or regions, near one, or both ends of the insulator, the rest of the wire extending through the bore of the insulator loosely or, in other words, in spaced relation to the wall of the passage.

In accordance with another feature of my invention the elasticity of the insulator is improved by a. median enlargement which is provided with a groove.

These and other features of my invention will be described in connection with the accompanying drawing in which Fig. 1 is a vertical section of a spark plug embodying my invention; and Fig. 2 is a vertical section of a spark plugv (in part broken away) provided with a modified housing.

As shown in the drawing, the spark plug includes a metal case i which is screw-threaded externally at its lower end for engagement with a screw-threaded oriilce in an internal combustion engine. The metal casing may consist v of two members a and b, which are threaded a soft alloy, such as the alloy described in -U. S.

Patent N0. 1,177,407 to Gilson, or of a textile material bonded with an artificial resin (Te'xtolite; and containing a lubrican such as graphite. The bulbous enlargement of the insulator 3i merges with smooth, non-anguler transition surface with a firing tip and externally pro-- jecting shaft A duct or passage extends longitudinally through the insulator for the reception of a conductor 8. A sparl terminal 9 projects from the of the ator into sparking relation with sparking terminal i projecting from the casing i. The conductor 8 is of somewhat lesserdiameter than. the diameter of the passage 7. conductor 8 and the wall of the passage l about three to six mils.

At the upper extremity the shaft 5, a flattened section of the conductor 8, as indicated at H, is fusion-sealed into the silica, a similar seal M being shown at the bottom. Seals of this type are well understood, being described in U. S. Patent No. 1,271,245 to Von Reckling hausen, patented July 2, 1918. It is desirable to have the main part of the conductor 8 consist of metal, for example, metal particularly adapted to resist high temperatures and erosion. With this object in view the conductors 9 and I0 may be plated with chromium. The sealed-in portion Ii, I2 of the conductor 8 may consist of.

conductor 8 as indicated, H and I 2, are fusionsealed into the silica leaving the main intermediate portion of the conductor 8 spaced from the wall of the passage so that expansion of the conductor due to heat will not cause cracking of the silica insulator. The lower seal 12 in some cases may be omitted, the space'around the wire 8 being open at the firing tip.

In order to further improve the yieldability of the insulator under pressure a groove or depression I3 is provided on the exterior of the spherical enlargement of the insulator 2. This depression may be produced by rolling during the fabrication of the insulator which may be carried out by process and apparatus described in U. S. Patent No. 1,814,205 patented June 13, 1933. The depression l3 may have adepth of about /64" to /64". If the groove is too shallow it may promote breakage of the insulator across the shaft 6 at its junction with the enlargement. If it is too deep the cracks will extend from the bearing between the gasket and the insulator to the bottom of the depression.

Surrounding the shaft 6 is a hood l5 which may consist of a suitable insulating material and is screwed into the shell member a. It is provided The clearance between the with vent holes It as illustrated. A light spring ll is provided between the external terminal it and the top of the shaft 6 of the insulator.

If the hood is to function as a radio shield, as well as a mechanical shield, it may be constructed in part of metal, for example, as shown in Fig. 2. As there illustrated, a short metal tube i9 is provided which is conveniently threaded to the spark plug shell Mounted upon this metal tube 59 is an insulating tube 20 into which projects a radio-shielded conductor M which leads to the electrical ignition system. ihis conduct-or 2i makes electrical connection to the spark plug terminal 22 through a connecting tube 23. The metal sheath 24, which surrounds the insulation 25 of the conductor at, is rounded. by a wire 26 to the metal member IQ of the spark plug shield. I What I claim as new and desire to secure by Letters Patent of the United States is:

1. A spark plug comprising an elongated insulator of vitreous material, said insulator having a longitudinally extending cavity, a conductor within said cavity, said conductor having a firing tip and having a diameter which is less than the diameter of said cavity whereby a clearance space is left between said conductor and the wall of said cavity, said conductor being sealed by local fusion of said insulator, and a casin surrounding said insulator consisting in part of metal and in part of insulating material, said parts engaging with one another.

2. A spark plug comprising an elongated silica insulator having a longitudinally extending cavity, a conductor within said cavity having a fir aorayzca ing tip projecting therefrom, the diameter of said conductor being less than the diameter of conductor within said cavity, with a clearance space from the wall of said cavity and having a firing tip projecting out of said cavity and being fusion-sealed into said silica insulator so as to leave clearance space adjacent said zenlargement of said insulator.

4. A spark plug comprising a casing, an elongated silica insulator mounted therein, said insulator having a longitudinal passage, a conductor having a lesser diameter than said passage and extending therethrough, said conductor having a flat, ribbon-shaped part sealed into said in.- sulator by fusion of the adjacent silica.

5. A spark plug comprising a casing, a silica insulator mounted therein, and having a longitudinal passage and a median enlargement, a conductor of lesser diameter than said passage extending through and projecting beyond said insulator, said conductor having at least one member of ribbon-shaped form which is fusionsealed into said insulator at a region remote from said enlargement leaving a clearance space about said conductor adjacent said enlargement.

PHILIP K. DEVERS. 

